The Pentagon is looking for emergency alternatives to its key Incirlik airbase in Turkey in case a diplomatic row with Ankara cuts off 70% of its airborne supplies to US forces in Iraq.

The possible loss of Turkish facilities follows US congressional criticism over alleged "genocide" against Armenian civilians by Ottoman Turkish forces during the First World War.

The dispute now threatens to turn into an international logistics and intelligence-gathering crisis if Ankara decides to impose sanctions over the use of its military facilities in retaliation.

The Turkish authorities allow the US to use the giant Incirlik base as a main supply hub for Iraq. Unmanned aerial drone spy missions over Iraq and Iran are flown from there.

They also allow overflights of Turkish territory by US transport aircraft, allowing them to reduce the risk of being shot down by insurgents inside Iraq's troubled northern provinces.

Pentagon officials confirmed yesterday that 70% of the military cargo sent to Iraq goes via Incirlik or on routes over Turkey.

It could take months to increase operations in other logistical hubs, including Jordan, Kuwait and at the Iraqi port of Umm Qasr in the northern Persian Gulf, the officials added.

Turkey, a leading member of Nato because of its common border with Russia, blocked US requests to allow part of its invasion force for Iraq to use Turkish territory in 2003, forcing planners to make last-minute changes to the plan to topple Saddam Hussein.

The Turkish government recalled its ambassador to Washington last week in protest against American criticism.

More than one million Armenians died as the Ottoman empire collapsed almost a century ago. The Turks claim that most died at the hands of Kurdish raiders or from hunger and disease rather than from deliberate attacks by Ottoman forces.

Banning the use of the Incirlik base and its wider airspace now depends on whether US lawmakers approve a draft resolution condemning the Armenian "genocide".